JPH10730A - Light reflective film - Google Patents

Abstract

(57) [Problem] An object of the present invention is to provide a light reflection film which is excellent in light reflectance and rich in whiteness while being a thin film. SOLUTION: In a light reflection film in which a metal thin film layer and a resin layer containing inorganic fine particles are sequentially laminated on one surface of a base film, the metal thin film layer is made of aluminum,
The refractive index n _f of the inorganic fine particles constituting the resin layer containing the inorganic fine particles and the refractive index n _{b of the} resin constituting the same layer are n _f −n
A light reflection film, wherein _b ≧ 0.4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a light reflecting film. More specifically, the present invention relates to a light reflection film that can be suitably used as a reflection plate of a liquid crystal display device of a portable information terminal such as a personal computer, a mobile phone, and a game machine.

[0002]

2. Description of the Related Art Liquid crystal display devices are used in a variety of applications such as OA equipment such as personal computers and word processors, video cameras, and televisions for vehicles. Recently, the use as small portable information terminals such as mobile phones and game machines has been rapidly increasing. In these portable applications, there is a demand for a lighter weight, smaller size, low power consumption and long-term use.
At present, a transmissive liquid crystal display device generally used uses a backlight as a light source, and it is said that the power consumption of the backlight portion occupies about 70% of the whole. In order to maintain high luminance over a long period of time, the capacity of the built-in battery needs to be increased, and this is a major problem for use in portable applications that require light weight and small size.

On the other hand, a reflection type liquid crystal display device that uses incident light from the surface of the display device as a light source does not require a backlight, and is suitable for portable use. A reflective film is used to reflect the incident light. Have been. In a transmissive liquid crystal display device using a backlight, a reflective film is used to more effectively use light from a light source as transmitted light. In both transmissive and reflective liquid crystal display devices, the display quality is high. A large amount of light is required to maintain and improve the image quality.

[0004] Conventional light-reflective films are formed by kneading and mixing a white pigment in a base material such as polycarbonate, styrene, polyester, or ABS resin, or by applying a paint in which the white pigment is dispersed on the surface of the base material. And a metal thin film of silver or the like provided by vapor deposition, or a coating of a paint in which a white pigment is dispersed is applied thereon. However, the film incorporating the white pigment,
From the viewpoint of maintaining the mechanical properties of the film, the amount of the pigment that can be filled is limited, and sufficient reflection performance cannot be obtained. Also,
A film coated with a white paint has a problem in that reflection efficiency is poor because the base film transmits light. On the other hand, a reflective film provided with a metal thin film has an extremely high total reflectance of light, but cannot provide uniform brightness when used in a liquid crystal display device because of the predominantly specular reflection and a small amount of diffuse reflection. Has disadvantages. In addition, silver thin films are chemically unstable, are easily oxidized by moisture in the air, and are prone to discoloration.In addition, they are also industrially expensive, and the same applies to silver thin films coated with white paint. There were drawbacks.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a light reflecting film which is thin and has excellent light reflectance and high whiteness.

[0006]

That is, a first aspect of the present invention is directed to a light reflecting film in which a metal thin film layer and a resin layer containing inorganic fine particles are sequentially laminated on one surface of a base film. made of aluminum, the refractive index n _b of the resin constituting the same layer and the refractive index n _f of the inorganic fine particles constituting the resin layer containing inorganic fine particles is n _f -n _b ≧ 0.4
It is a light reflection film characterized by these.

A second invention is the light reflection film according to the first invention, wherein the inorganic fine particles are rutile type titanium dioxide.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail. The base film used in the present invention includes various types such as a polycarbonate film, a polyethylene film, a polypropylene film, a polyethylene terephthalate film, a polyvinyl chloride film, a polystyrene film, a polyamide film, a polyethylene naphthalate film, a polyether sulfone film, and a polyacrylate film. And any of these can be appropriately selected and used. The thickness of the base film is not particularly limited, but is preferably in the range of 5 μm to 100 μm in consideration of the thickness of the final light reflection film or the handleability.

In the present invention, the metal thin film layer provided on the base film has high total reflectance, is chemically stable due to the property of forming a thin oxide film called a passivation layer on the surface, and is industrially suitable. It is preferable to use inexpensive aluminum. When silver, which has a high total reflectance, is used as a metal other than aluminum, it has excellent reflection performance, but is chemically unstable, is easily oxidized by moisture in the air, and is liable to be discolored. Not preferred.

In the present invention, as a method for forming a metal thin film layer made of aluminum on a base film, a method such as vacuum deposition, sputtering, or ion plating is used.
A method called VD (physical vaper deposition) or a method called CVD (chemical vaper deposition) such as high-frequency plasma or microwave plasma can be used. The thickness of the aluminum thin film layer is preferably 300 to 3000 angstroms,
More preferably, the thickness is from 00 to 2000 Å. When the thickness is less than 300 angstroms, the reflectance tends to decrease. When the thickness is more than 3000 angstroms, the effect of improving the reflectance cannot be expected so much, and the productivity tends to deteriorate.

In the present invention, the resin used for the resin layer containing inorganic fine particles includes, for example, polyester resins, acrylic resins, alkyd resins, and the like commonly used for paints.
Cellulose resin, urethane resin, amino resin, epoxy resin, phenoxy resin, polyvinyl acetal resin,
Examples thereof include polyvinyl butyral resin, fluorine resin, and silicone resin, and these can be used alone or in combination of two or more. The form of these resins is not particularly limited as long as they can be applied such as a solution type or an emulsion type.

The inorganic fine particles used in the present invention include, for example, titanium dioxide, zircon oxide, zinc sulfide, zinc oxide,
Examples thereof include antimony oxide and magnesium oxide, and these can be used alone or in combination of two or more. Among them, rutile titanium dioxide is particularly preferable. The combination of the inorganic fine particles and the resin used in the resin layer containing the inorganic fine particles of the present invention is selected such that the refractive index n _f of the inorganic fine particles and the refractive index n _{b of the} resin satisfy n _f −n _b ≧ 0.4. It is important to. When n _f −n _b <0.4, refraction and scattering of light at the interface between the inorganic fine particles and the resin are unlikely to occur, so that sufficient reflection performance cannot be obtained. The average particle diameter of the inorganic fine particles used in the present invention is 0.1 to 3
μm is preferred. When the average particle diameter is 0.1 μm or less, the light scattering ability is remarkably reduced because it is 可視 or less of the wavelength of visible light. On the other hand, if it is 3 μm or more, the dispersibility in the resin is extremely poor, and this is not preferable from the viewpoint of workability such as sedimentation in the paint.

The content of the inorganic fine particles in the resin layer containing the inorganic fine particles is 1 to 100 parts by weight of the resin.
It is preferably from 5 to 85 parts by weight, more preferably from 45 to 75 parts by weight. If the content is 15 parts by weight or less, the amount of the pigment is too small, the light scattering is insufficient, and it is difficult to obtain the intended reflection performance. If the content is more than 85 parts by weight, the amount of light absorbed by the pigment increases and the reflection performance deteriorates. Not only that, there is a tendency for problems in hardness and adhesion of the coating film due to insufficient resin components.

In the present invention, a paint shaker, a roll mill, a sand mill, a ball mill, an attritor, a jet mill, a homogenizer, and the like can be used in the step of dispersing the inorganic fine particles and the resin. Further, for the purpose of improving dispersibility in the dispersion step, silane-based, titanate-based, zircoaluminate-based coupling agents and metal chelates, organometallic compounds such as metal alkoxides,
Alternatively, a commercially available resin type dispersant such as Solsper
s24000 (manufactured by Zeneca Corporation), Disperby
You may add k-160, 161 (made by Big Chemie), etc.

In the present invention, a coating method for sequentially laminating a resin layer containing inorganic fine particles on an aluminum thin film layer includes a gravure coater, knife coater, wire bar coater, doctor blade coater, reverse roll coater, dipping coater, and the like. An air knife coater, a die coater or the like can be used. The thickness of the resin layer containing the inorganic fine particles is preferably 5 to 50 μm. When the thickness is 5 μm or less, light scattering is insufficient and it is difficult to obtain the intended reflection performance. Even when the coating is applied to 50 μm or more, not only the remarkable improvement in the reflection performance is not seen but also the productivity is deteriorated, which is not preferable.

In the light reflecting film of the present invention, incident light is first diffused and reflected by the inorganic fine particles in the resin layer containing the inorganic fine particles. Next, a part of the light transmitted through the resin layer containing the inorganic fine particles is reflected on the surface of the metal thin film layer made of aluminum. This reflected light is emitted while being refracted and scattered again by the inorganic fine particles in the resin layer containing the inorganic fine particles. As described above, the light reflection film having uniform and high reflection performance can be obtained by the synergistic effect of the diffuse reflection by the inorganic fine particles and the surface reflection of the aluminum layer.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described based on embodiments. In the example,
“Parts” and “%” are “parts by weight” and “% by weight”, respectively. Example 1 A 1000 angstrom aluminum thin film layer was formed on one surface of a 50 μm-thick polyethylene terephthalate film by DC sputtering. 82.5 parts of titanium dioxide (manufactured by Ishihara Sangyo Co., Ltd., Taipaque CR97, refractive index 2.7) 112.5 parts of fluororesin (manufactured by Asahi Glass Co., Ltd., Lumiflon LF200, refractive index 1.45) Xylene 52.5 A composition comprising 52.5 parts of methyl isobutyl ketone was kneaded and dispersed with a paint shaker for 30 minutes to obtain a coating liquid for forming a resin layer containing inorganic fine particles. The coating liquid was applied on the aluminum thin film layer formed on the polyethylene terephthalate film with a wire bar coater to obtain a light reflection film having a configuration as shown in Table 1.

Comparative Example 1 As a comparison with Example 1, the coating liquid obtained in Example 1 was applied to one surface of a polyethylene terephthalate film having a thickness of 50 μm by a wire bar coater, and an aluminum thin film as shown in Table 1 was obtained. A light reflection film having no layer was obtained.

Example 2 55 parts of titanium dioxide (Taitone R42, manufactured by Sakai Chemical Industry Co., Ltd., refractive index 2.7) 45 parts of cellulose acetate butyrate resin (CAB551-0.01, manufactured by Eastman Kodak Company, refraction) The composition consisting of 50 parts of toluene and 50 parts of methyl isobutyl ketone was kneaded and dispersed with a paint shaker for 30 minutes to obtain a coating liquid for forming a resin layer containing inorganic fine particles. The coating solution was applied on the aluminum thin film layer described in Example 1 with a wire bar coater to obtain a light reflection film having a configuration as shown in Table 1.

Comparative Example 2 As a comparison of Example 2, the procedure of Example 2 was repeated except that the titanium dioxide used in Example 2 was changed to barium sulfate (B-30, manufactured by Sakai Chemical Industry Co., Ltd., refractive index 1.65). The same operation as in Example 2 was performed to obtain a light reflection film having a configuration as shown in Table 1.

Comparative Example 3 A comparison was made between Examples 1 and 2 without providing a resin layer containing inorganic fine particles on the aluminum thin film layer described in Example 1.

The reflectance at 550 nm of the light reflecting films obtained in the above Examples and Comparative Examples was measured with a spectrophotometer (Spectrophotometer UV-256FW, manufactured by Shimadzu Corporation). In addition, a colorimeter (manufactured by Nippon Denshoku Co., Ltd., SZ- # 9)
The whiteness W was obtained from the lightness index L and the perceived chromaticity indices a and b measured in 0) according to the following equation. Whiteness is considered an index of uniform diffuse reflection performance. Table 1 shows the evaluation results. W = 100 − {(100−L) ² + (a ² + b ² )}
^0.5

[0023]

[Table 1]

In Example 1 and Comparative Example 1, Example 1 in which a metal thin film layer made of aluminum was provided had a higher reflectance and better reflectance.
Both whiteness improved. In Example 2 and Comparative Example 2, the difference between the refractive index of the inorganic fine particles constituting the resin layer containing the inorganic fine particles and the refractive index of the resin constituting the same layer was 0.4 or less. Example 2 having a refractive index difference of 0.4 or more improved both reflectance and whiteness. In Examples 1 and 2 and Comparative Example 3, Comparative Example 3 in which the resin layer containing the inorganic fine particles was not provided had a high reflectance but a significantly low whiteness.

[0025]

The light reflecting film of the present invention has a structure in which a metal thin film layer made of aluminum and a resin layer containing inorganic fine particles are sequentially laminated on one surface of a base film, and the refractive index of the inorganic fine particles is n. _f and the refractive index n _{b of the} resin are n _f −n _b
By selecting the material so as to satisfy ≧ 0.4, the reflection efficiency is improved, and a higher reflection performance is obtained compared to a light reflection film or a metal vapor deposition film in which a white paint is directly applied to a conventional transparent base film. Was completed.

[Brief description of the drawings]

FIG. 1 shows an example of the structure of the light reflecting film of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Base film 2 Metal thin film layer made of aluminum 3 Resin layer containing inorganic fine particles

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location G02B 5/08 G02B 5/08 A

Claims (2)

[Claims] 1. A light reflection film in which a metal thin film layer and a resin layer containing inorganic fine particles are sequentially laminated on one surface of a base film, wherein the metal thin film layer is made of aluminum,
The refractive index n _f of the inorganic fine particles constituting the resin layer containing the inorganic fine particles and the refractive index n _{b of the} resin constituting the same layer are n _f −n
A light reflection film, wherein _b ≧ 0.4. 2. The light reflecting film according to claim 1, wherein the inorganic fine particles are rutile type titanium dioxide.